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Viagra impotence pills. Forceps holding a 50 mg Viagra pill (sildenafil citrate) used to treat male impotence. Viagra is the first oral pill for impotence. Unlike other treatments that directly cause penile erections, Viagra affects the response to sexual stimulation. Viagra enhances the smooth muscle relaxant effects of nitric oxide, a substance normally released in response to sexual stimulation. Smooth muscle relaxation allows blood to enter the penis leading to an erection. The recommended dose is 50mg taken one hour before sexual activity; 25mg and 100mg pills are also available. Viagra, made by Pfizer Pharma- ceuticals, was approved for use in USA in 1998.